Woods such as a zelkova, a Japanese oak, etc., have been widely used for floor materials, etc., owing to visual and feeling characteristics such as the beauty of the grain of wood and mild feeling of wood, etc. Also, woods such as a Honduras rose wood, a Yellow Birch, etc., have largely used as the sound plate, which is a sound generating portion of a marimba, a xylophone, etc., owing to the hardness of the surface thereof and the good sound tone. However, since such precious trees become gradually few, increase the scarecity value thereof, and become expensive, the development of a process of increasing the quality of low grade woods having inferior appearance and soft surface have recently been desired.
Hitherto, for improving the beautiful appearance, surface hardness, abrasion resistance and water resistance, etc., of wood, a process of applying a so-called wood plastic combination (WPC) treatment, that is, a treatment of impregnating wood with a thermosetting resin at reduced pressure or under pressure and curing the resin by heating under pressure is known. However, in the WPC treatment, the process is complicated, the equipment becomes large, and the product cost becomes high. Also, in the WPC treatment, a resin film is not formed on the surface of the treated wood and hence the surface hardness of the product is low.
Also, there is a process of overlaying a paper impregnated with a thermosetting resin on the surface of a wood. However, in the process, the resin impregnated in a nonwoven fabric, a paper or a cloth is inferior in fluidity, which results in causing such difficulties that a floating phenomenon occurs on the surface of a wood having large vessel or tracheid as a fault of the coated surface and also the adhesion becomes inferior.
Furthermore, there is a process of directly coating the surface of wood with a thermosetting resin. In this case, the process is suitable for coating the highly uneven surface of a vessel, etc. However, the process has a disadvantage that the viscosity of the resin reduces suddenly during hot-press molding and the resin oozes out from the side surface of the wood to outside. Also, the process has a further disadvantage that the product formed is poor in cracking resistance and the resin layer formed in the surface is liable to be cracked.